1. Field of the Invention
This invention relates to sonar systems and, more particularly, to a side scan sonar system which records the port data channel from right to left and the starboard data channel from left to right utilizing a continuous transverse belt carrying a writing stylus.
2. Description of the Prior Art
Two basic acoustic approaches are used to distinguish topographic features or objects on the sea floor. The first method is echo sounding which employs a vertical axis acoustic beam. Another method, called side looking or side scanning sonar, requires an acoustic beam whose main axis is slightly below horizontal. The beam is very narrow in the horizontal plane, yet sufficiently broad in the vertical plane to obtain echoes from a point on the sea floor directly below the transducer to points a large distance abeam of the transducer. The combination of the beam shape and the very short length of the acoustic pulse gives side scan sonars the capabilities to resolve small topographic irregularities and small objects on or above the sea floor. As the transducer is towed at an appropriate depth behind a towing vessel, the reflected echoes are graphically recorded to present a topographic or plan view mapping. The echoes are generally recorded on a strip chart recorder of which two basic varieties exist. In the first variety, both left channel and right channel data is recorded from left to right on the chart with the left channel recorded from the left edge toward the center and the right channel recorded from the center toward the right edge. The primary disadvantage of this variety of recorder is that, for left channel data, the spatial relationships between the echoes on the chart with respect to each other and a reference point corresponding to the transducer is the reverse of the spatial relationships between the topographical features producing the echoes with respect to each other and the transducer. Consequently, the display is somewhat confusing and thus difficult to read. The other variety of recorder records left channel data from center to left and right channel data from center to right. This recorder, which is sold by the Environmental Equipment Division of EG&G of Waltham, Massachusetts, uses dual helix electrodes which sweep out from the center of the recording drum as the drum rotates. Electrosensitive chart paper is placed between the recording drum and a transverse knife electrode so that the points of contact between the helixes and the knife sweep out from the center of the recording drum as the recording drum rotates. The helix on the right prints echoes from the starboard transducer while the helix on the left prints echoes from the port transducer. The primary problem with this system is that the knife quickly wears because of the current flowing from the knife to the helixes responsive to the returns generated by the watertransducer interface.